I withdrew a lot of cash every month so far, do I need to wait until salary day to apply UK visa? [duplicate]

You say you withdraw large sums in cash after receiving your salary, because the nearest ATM is inconvenient and your living costs are mostly paid in cash. This is reasonable in itself. But you say that you leave around 100 SGD (around £50) in the bank each month, while in the comments you say that you have over 4000 SGD in cash.

You have 4000 SGD in cash when your salary is 3000 SGD. You've given a clear and understandable explanation of why you withdraw large sums in cash, but if you currently have 1.3x your monthly salary in cash then these withdrawals are clearly far more than you actually need.

The person processing your application can't tell the difference between withdrawn cash that you spend during the month and withdrawn cash that you keep around at home, and will assume that everything you withdraw is being spent on your normal living costs. If you leave the same amount each month, they will see that you have only a very small balance at the end of every month, and your salary appears to leave no room for anything outside your cost of living. This will make it very hard for you to convince them that you can afford the trip you are planning.

Waiting until the day you receive your salary won't make a meaningful difference. They're not stupid, they know that people have more money immediately after they get paid than immediately before they get paid. When they look at your finances they're not checking to see just how much money you have (that is relevant, but not the only thing they want to see), they want to see a consistent pattern of income and outgoings over a longer period (at least 3 months, ideally 6 months), to demonstrate that you are living within your means and have an appropriate budget available for the trip.

My advice would be to start withdrawing only what you actually need for living expenses, and allow the rest to remain in your bank account. Do this for several months, building up a meaningful level of savings (this doesn't have to be huge, but must be enough to comfortably cover the costs of your planned trip). This will demonstrate to the person processing your application that you do indeed have a financial situation that makes this trip practical.

See also (as linked by Zach in the question comments) the question: Should I submit bank statements when applying for a UK Visa? What do they say about me? for a much deeper explanation of what they want to see (and what they do not want to see) when they look at your bank account.